Identification of a Rhythmic Firing Pattern in the Enteric Nervous System That Generates Rhythmic Electrical Activity in Smooth Muscle

Abstract

The enteric nervous system (ENS) contains millions of neurons essential for organization of motor behavior of the intestine. It is well established that the large intestine requires ENS activity to drive propulsive motor behaviors. However, the firing pattern of the ENS underlying propagating neurogenic contractions of the large intestine remains unknown. To identify this, we used high-resolution neuronal imaging with electrophysiology from neighboring smooth muscle. Myoelectric activity underlying propagating neurogenic contractions along murine large intestine [also referred to as colonic migrating motor complexes, (CMMCs)] consisted of prolonged bursts of rhythmic depolarizations at a frequency of ∼2 Hz. Temporal coordination of this activity in the smooth muscle over large spatial fields (∼7 mm, longitudinally) was dependent on the ENS. During quiescent periods between neurogenic contractions, recordings from large populations of enteric neurons, in mice of either sex, revealed ongoing activity. The onset of neurogenic contractions was characterized by the emergence of temporally synchronized activity across large populations of excitatory and inhibitory neurons. This neuronal firing pattern was rhythmic and temporally synchronized across large numbers of ganglia at ∼2 Hz. ENS activation preceded smooth muscle depolarization, indicating rhythmic depolarizations in smooth muscle were controlled by firing of enteric neurons. The cyclical emergence of temporally coordinated firing of large populations of enteric neurons represents a unique neural motor pattern outside the CNS. This is the first direct observation of rhythmic firing in the ENS underlying rhythmic electrical depolarizations in smooth muscle. The pattern of neuronal activity we identified underlies the generation of CMMCs. How the enteric nervous system (ENS) generates neurogenic contractions of smooth muscle in the gastrointestinal (GI) tract has been a long-standing mystery in vertebrates. It is well known that myogenic pacemaker cells exist in the GI tract [called interstitial cells of Cajal (ICCs)] that generate rhythmic myogenic contractions. However, the mechanisms underlying the generation of rhythmic neurogenic contractions of smooth muscle in the GI tract remains unknown. We developed a high-resolution neuronal imaging method with electrophysiology to address this issue. This technique revealed a novel pattern of rhythmic coordinated neuronal firing in the ENS that has never been identified. Rhythmic neuronal firing in the ENS was found to generate rhythmic neurogenic depolarizations in smooth muscle that underlie contraction of the GI tract.

Akt phosphorylation of neuronal nitric oxide synthase regulates gastrointestinal motility in mouse ileum

“…We found no direct studies of Akt activation by depolarization in enteric neurons, however, and the relevance of depolarization frequency for GI motility has not been reported. Recent work examining myenteric plexus Ca 2+ waves suggests a wide depolarization frequency range (0.2 to 1.3 Hz) for nitrergic neurons that overlaps the 0.25 to 0.5 Hz EFS at which we saw Akt inhibitor effects (16). Importantly, our results show that Akt-dependent nNOS S1412 augmentation of nitrergic relaxation is detected only when intracellular [Ca 2+ ] is expected to be low.…”

“…nNOS S1412 phosphorylation may sustain NO synthesis beyond the brief depolarization of neurons (16,17), but S1412 does not appear relevant at saturating [Ca 2+ ] during high-frequency depolarization (51). nNOS S1412 tunes increased NO production to low resting [Ca 2+ ], thereby integrating several cellular signals.…”

“…Elevated neuronal intracellular [Ca 2+ ] is therefore a major stimulus for nitrergic relaxation (14). Sustained high [Ca 2+ ] can damage cells (15), so generally only brief depolarization transiently activates Ca 2+ entry (16). Because GI myocyte relaxation is prolonged (>5 s) (17), nNOS posttranslational modification may sustain NO production independently of Ca 2+ entry.…”

Vermeidung von Clustering und Urge bei der chirurgischen transanalen Therapie der distalen tiefen Rektozele

“…Anatomisch findet sich eine Zweiteilung in den Plexus submucosus und den Plexus myentericus, der maßgeblich die Aktivität der Muskulatur steuert. Die Kommunikation zwischen enterischen Nervenzellen wird durch Interneurone sichergestellt, die Millionen von synaptischen Verbindungen im ENS aufrechterhalten [20]. Diese synaptischen Verbindungen ermöglichen sowohl die Initiierung vorwärts als auch rückwärts gerichteter Peristaltik.…”

Protein kinase A facilitates relaxation of mouse ileum via phosphorylation of neuronal nitric oxide synthase

“…We recently showed that low frequency depolarization relaxes mouse ileum via Akt phosphorylation of nNOS S1412 (D.D. Guerra et al, ); this may explain why NO responses are tuned to depolarization frequency in the gut (Spencer et al, ) and why nitrergic inhibitory junction potentials (IJPs) have a longer duration than action potentials (Hurt et al, ; Keef et al, ).…”